The present invention is directed to a process and a plant for slurrying and oxidation of a petroleum resid with water. More particularly, the invention is directed to integrating the slurrying with oxidation, by prilling the resid at an elevated temperature to form liquid particles of the resid in a gaseous medium and directly quenching the particles with cooling water to form a pumpable slurry for oxidation.
As the maturity of petroleum refining progresses, more and more of the crude oil is converted to useful light products. The bottom of the barrel, petroleum resid, becomes more and more difficult to dispose of in an economical, useful manner. The residue from petroleum refining has a wide number of uses, including paving asphalt, fuel and feedstock for gasification to form a synthesis gas. Each of these uses for the resid has a number of disadvantages. Paving grade asphalt used in road construction must meet a number of specifications, including viscosity (usually 200-5000 poises at 60xc2x0 F.), penetration (usually greater than 30 to 200 dmm), penetration ratio 15xc2x0 F./25xc2x0 F. (usually above about 0.3), ductility, temperature susceptibility, and others. Because of the narrow specifications for paving asphalt, it is becoming more and more difficult for resids to meet the needed paving asphalt specifications.
In contrast to paving asphalt, the specifications for petroleum resid that is burned as a fuel or used as feed in a partial oxidation gasifier, are less stringent. The resid generally has a higher calorific value and better combustion characteristics compared to coal and petroleum coke. Unfortunately, heavy resid poses storage and handling problems for use as a liquid fuel since it must be kept at an elevated temperature or a high value lighter hydrocarbon is used as a diluent to keep it in liquid state.
In the gasification of resid, it is also typical for water or steam to be introduced into the gasifier as a temperature moderator and hydrogen source. In the gasification of coal and coke, these materials are commonly supplied to the gasification reactor in the form of a water slurry. Much work has gone into formation and maintenance of the coke/coal slurry. The coal or coke is usually ground to a fine particle size and mixed with water to make a pumpable slurry. Factors such as particle size and water content are usually critical to obtain a pumpable slurry which can be supplied to the gasification reactor. For example, if the particle size is too large or the water content is too low, the viscosity of the slurry will be too high to be easily pumped. On the other hand, if the water content is too high, it may be necessary to supplement the feed to the gasification reactor with a liquid hydrocarbon feedstock. Various references discussing slurrying of coke and/or coal for gasification or combustion include U.S. Pat. No. 3,996,026 to Cole; U.S. Pat. No. 4,526,588 to Lusch et al; U.S. Pat. Nos. 4,657,702 and 4,681,700 to Vasconcellos et al; U.S. Pat. No. 4,950,307 to Najjar et al; and WO 97/05216 to Isentropic Systems Ltd.
U.S. Pat. No. 5,478,365 to Nikanjam et al discloses a combustible heavy hydrocarbon-in-water emulsion containing a phosphate ester, a high molecular weight thickener, a high softening point hydrocarbon material and 25-50 weight percent water. The emulsion is made in a colloid mill by mixing the components at an elevated temperature and pressure to keep the hydrocarbon material from solidifying and the water from vaporizing, and then cooling the emulsion.
U.S. Pat. No. 4,931,231 to Teppo et al discloses a method for manufacturing discrete pellets of asphaltic material by flowing the asphaltic material in molten form as an elongated annular stream directly into cooling water to solidify and shatter the elongated stream into discrete solid particles. The particles formed as a result of shattering are not spherical and have undesirable flow and/or handling characteristics.
A pelletizer apparatus and method for pelletizing a hard petroleum resid is disclosed in our earlier copending application U.S. Ser. No. 09/447,408, filed Nov. 23, 1999. This disclosure involves the prilling of the resid at a temperature at which it is liquid, allowing the resid particles to form a substantially spherical shape, and then quenching the particles to solidify them in their spherical shape.
In the present invention liquid asphaltenes from solvent desasphalting or another petroleum resid material are pumped to an extrusion device to produce liquid particles in a gaseous medium that are quenched with water to form a slurry of hydrocarbon particles of the appropriate size distribution suitable for pumping and combustion/gasification without further grinding or processing.
In one aspect, the present invention provides a process for the slurrying and oxidation of a petroleum resid, comprising the steps of:
(a) heating petroleum resid to a temperature at which it is in a liquid state;
(b) forming the resid into finely divided particles in a gaseous medium;
(c) directly quenching the resid particles with water to form a pumpable slurry of solidified resid particles; (d) pumping the slurry to an oxidation reactor; and
(e) injecting the slurry into the oxidation reactor and oxidizing the resid in the reactor. The resid preferably has a softening point temperature above about 185xc2x0 F. The process can also include solvent deasphalting a petroleum residue to form a deasphalted oil fraction, an optional resin fraction and an asphaltene fraction, and supplying the asphaltene fraction as the petroleum resid for the heating step (a).
The particle-forming step (b) and the quenching step (c) preferably comprise: (1) continuously feeding the liquid petroleum resid from step (a) to an inlet of a centrifugal prilling head comprising a plurality of radially arrayed discharge orifices; (2) rotating the prilling head to discharge liquid petroleum resid from the orifices into free space at an upper end of a prilling vessel having a diameter larger than a throw-away diameter of the discharged petroleum resid; (3) allowing the discharged resid to break apart and form into particles in a high temperature zone of the prilling vessel at which the petroleum resid is liquid and fall downwardly into a water bath maintained at a temperature effective to solidify the particles and form the pumpable slurry; and (4) withdrawing the slurry from the prilling vessel. The discharge orifices are preferably arrayed at a circumference of the prilling head in a plurality of vertically spaced upper and lower rows wherein the lower row or rows are disposed at a smaller radius from an axis of rotation of the prilling head than the upper row or rows. The prilling head can have a circumference tapered from an uppermost row to a lowermost row. Preferably, the prilling head is rotated at from about 200 to about 10,000 rpm, the prilling head has a diameter from about 2 inches to about 5 feet, the orifices have a diameter from about {fraction (1/32)}-inch to about 1-inch and a capacity of from about 1 to about 1000 lbs/hr of resid per orifice, the throw-away diameter is from about 1 foot to about 15 feet and the particles have a size range larger than about 0.01 mm and smaller than about 1 mm.
The water bath is preferably maintained in the prilling vessel at a temperature from about 40xc2x0 to about 190xc2x0 F. The water can be introduced into the prilling vessel as an inwardly directed spray in a cooling zone above the water bath to at least partially cool the particles before they enter the bath. The quenching water can pass once through the prilling vessel, essentially free of recirculation, and wherein the slurry from the prilling vessel has a solids content from 50 to 80 percent. If necessary, water can be added to or removed from the slurry and recirculated to the prilling vessel. A dispersant can be admixed into the slurry to aid pumpability. The slurry can have an apparent viscosity less than about 2000 cSt, and preferably comprises from 60 to 70 weight percent solids and has an apparent viscosity from about 100 to about 300 cSt. The particles preferably have a size less than 0.05 mm.
The oxidation reactor can be a gasifier that converts the petroleum resid to synthesis gas, or a combustion reaction that burns the petroleum resid to produce steam. The gasification reactor can be a high temperature, entrained flow, slagging type, oxygen or air blown gasifier operated at a temperature from about 1800xc2x0 to about 2600xc2x0 F. and a pressure from about 400 to about 1200 psig.
In another aspect, the present invention provides a plant for petroleum refinery bottoms processing. The plant includes an atmospheric distillation unit, a solvent deasphalting unit, a slurrying unit and an oxidation reactor. The atmospheric distillation unit fractionates atmospheric tower bottoms into naphtha, diesel and atmospheric resid fractions. The solvent deasphalting unit separates the atmospheric resid fraction into a deasphalted oil fraction and an asphaltene fraction. The slurrying unit forms the asphaltene fraction into finely divided particles in a gaseous medium at a temperature at which the asphaltene fraction is liquid, and directly quenches the particles with water to form a pumpable slurry of solidified asphaltene particles. The oxidation reactor at least partially oxidizes the asphaltene particles at elevated temperature. One or more pumps are provided for pumping a stream of the slurry from the slurrying unit to the oxidation reactor.
The asphaltene slurry stream preferably comprises from about 50 to about 80 weight percent solids, has a viscosity less than about 2000 cSt, and the asphaltene particles are substantially between 0.01 and 1 mm. The asphaltene slurry stream preferably includes from 1 ppmw up to 2 weight percent of a non-foaming dispersant.
The slurrying unit preferably comprises an upright prilling vessel having an upper prilling zone, a hot discharge zone below the prilling zone, a cooling zone below the discharge zone, and a lower cooling bath below the cooling zone. A centrally disposed prilling head in the prilling zone is rotatable along a vertical axis and has a plurality of discharge orifices for throwing asphaltene radially outwardly. A throw-away diameter of the prilling head is less than an inside diameter of the prilling vessel. A line supplies a hot, liquid asphaltene stream comprising the asphaltene fraction to the prilling head. A heater can be used for heating the asphaltene stream supplied to the prilling head. The vertical height of the discharge zone is sufficient to allow asphaltene discharged from the prilling head to form into liquid droplets. Nozzles are provided for spraying water inwardly into the cooling zone to cool and at least partially solidify the liquid droplets to be collected in the bath and form a slurry of solidified asphaltene particles in the bath. A line supplies water to the nozzles and the bath to maintain a depth of the bath in the prilling vessel. Another line is provided for withdrawing the slurry of the asphaltene particles in the bath water from the prilling vessel.
The discharge orifices are preferably arrayed at a circumference of the prilling head in a plurality of vertically spaced upper and lower rows wherein the lower row or rows are disposed at a smaller radius from the axis of rotation of the prilling head than the upper row or rows. The prilling head can have a circumference tapered from an uppermost row to a lowermost row. The prilling head can have a plurality of rings of different diameter with orifices formed in an outer circumference of each ring, wherein the rings are secured to the prilling head in a descending fashion wherein each successively lower ring has a smaller diameter than the preceding ring. A drive can rotate the prilling head at from about 200 to about 10,000 rpm. The prilling head preferably has a diameter from about 6 inches to about 5 feet, and the orifices lo have a diameter from about {fraction (1/32)}-inch to about 1-inch and a capacity of from about 1 to about 1000 lbs/hr of asphaltene per orifice.
The prilling vessel can also have a conical bottom containing the bath and a discharge at a lower end of the conical bottom for feeding the slurry into the withdrawal line.
The oxidation reactor can be a gasifier or a combustion reactor.